1. Field of Invention
The invention relates to a printing device for paper handling applied to print data and/or records on paper, and especially relates to a double-sided printing device for paper handling.
2. Related Art
Conventional printing apparatuses are fax machines, printers and photocopiers, and printers can be furthermore classified as dot matrix, ink jet and laser printers. In accordance with the mechanisms of paper-picking, they can also be classified as front and back input tray printers.
Recycled paper is often used with printers, and it is preferable to use both sides of a sheet of paper when printing. But because the papers are re-used, they often become jammed inside the printer during the process of paper-picking, which wastes time and can damage the printer. If both sides of a sheet of paper are used for printing less paper is wasted.
In order to overcome the above problems some inventions have been proposed, such as U.S. Pat. Nos. 6,167,231 and 6,332,068. Although by these two inventions double-sided printing is achieved, some problems still occur and are described as follows:
1. The designs of the double-sided printing devices of the previous inventions are only useful for the front input tray printers but not for the back input tray printers.
2. The designs of the double-sided printing devices of the previous inventions are oriented externally. The production cost for these devices is increased.
The object of the invention is to provide a double-sided printing device in order to overcome the above problems. The device of the invention is designed internally and is driven by a single drive so that the production cost can be decreased.
The double-sided printing device proposed by the invention comprises a holding unit, a first switch, a drive, a printing unit, a turning unit, an obstructing unit and a second switch. Some papers are placed in the holding unit, the first switch is driven by the reverse rotation of the drive to couple with the holding unit such that a sheet of paper placed in the holding unit is pulled out and by the ordinary rotation of the drive is fed into the printing unit so that printed data can be printed on its front side.
After completing the printing on the front side of the sheet of paper, the second switch is driven by another reverse rotation of the drive to couple with the turning unit such that the sheet of paper is guided into the turning unit and turned over. At this time the obstruction unit is applied to stop the first switch from coupling with the holding unit to prevent it from feeding papers repeatedly. Finally the drive rotates normally to pull the second switch to free from the turning unit so that the sheet of paper can be fed into the printing unit and the printed data can be printed on the back side of the sheet of paper.
A page sensor can also be applied to actuate the obstructing unit to reduce control problems. The page sensor is set on the path for paper handing and when a sheet of paper goes through it, it is initiated to push the obstructing unit to function normally.
Further scope of applicability of the invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.